Computational and Experimental Study of Deep Stall in a Generic T-Tail Transport Aircraft

A significant amount of effort has been invested over the past twenty years in improving the understanding of airliner upset, from the perspective of aerodynamics, flight dynamics and control law design, and pilot training. A challenge in these endeavours is to obtain mathematical models of sufficient fidelity to be deployed in simulation, analysis and design. Furthermore, once such a wide-envelope model is generated for the aircraft of interest it will inevitably display dynamics that is nonlinear in the post-stall upset regime, making it difficult to gain a deep understanding of the behaviour and its dependence upon parameter variations. This paper compares flight test responses of a sub-scale remotely piloted physical model of the NASA GTT (Generic T-Tail) aircraft under upset/deep stall conditions with behaviour inferred from computational studies. The latter includes both the NASA aerodynamic dataset and aerodynamic data based on further wind tunnel testing. It is found that the oscillatory dynamics leading to asymmetric deep stall can be difficult to predict and to interpret from flight tests but that the latter yields behaviour that is qualitatively very similar to that inferred from the bifurcation diagrams.